This invention is directed to combustion apparatus such as is used in a gas turbine engine, and particularly to a combustion liner structure for such an apparatus.
Gas turbine combustion apparatuses typically include a liner in which combustion is conducted. Such liners ordinarily are of circular or of annular cross-section, with an upstream end called a dome and an outlet at the downstream end for combustion products in flow communication with the turbine inlet. Fuel is introduced at the upstream end and air enters the liner through the upstream end and through the sidewall of the liner to effect combustion and to dilute the combustion products to a suitable temperature.
Although gas turbine combustion liners are typically made of high temperature resisting metal alloys, some combustion apparatuses have been made with walls constructed of various ceramic materials (U.S. Pat. No. 1,827,246 -- Lorenzen; U.S. Pat. No. 3,594,109 -- Penny; U.S. Pat. No. 3,880,574 -- Irwin; U.S. Pat. No. 3,880,575 -- Cross et al.; and published Application No. B377,172 -- Holden).
While various known ceramics are highly resistant to heat and may be formed into cylinders and other shapes by known techniques, such materials are relatively weak and brittle. Also, ceramic materials have relatively low thermal expansion coefficients, which presents a problem when it becomes necessary to mount them in conjunction with metal components in a combustion apparatus.
Silicon nitride and silicon carbide are typical of the ceramic materials utilized in the prior art, but the nature of the ceramic is a matter of choice providing that the requisite high temperature physical properties and corrosion resistance are obtained.
When gas turbine combustors are made with heat resistant alloy liners, considerable air cooling is required to provide durability at current operating conditions. It is desirable to increase the firing temperature and as this is done, a larger fraction of the air flow is needed for combustion resulting in increased heat transfer to the liner. This will preclude the use of conventional designs for increased firing temperatures, especially when low energy content fuels (e.g., low BTU coal gas) are utilized, which need nearly all of the air for the actual combustion. Thus, there is a developing need for the use of ceramics to accommodate increased firing temperatures, but integration of these materials into a combustion system must be done in a manner that will accommodate the brittle nature of these materials.